Jin Kyung-joon was acquitted on separate bribery charges over making the founder of online game publisher Nexon pay for his acquisition of the company's unlisted stocks in 2005, Seoul Central District Court spokesman Shin Dae-hwan said.
Jin made millions of dollars in profit last year after he sold his shares in Nexon Japan, which went public in 2011.
According to the court, Jin, in exchange for closing an investigation over suspected business irregularities at Korean Air in 2010, pressured the airline's then-vice president to hire the cleaning services of a company run by his brother-in-law.
Prosecutors said Jin received 400 million won ($343,000) from Nexon founder Kim Jeongju in 2005 to buy unlisted company shares and later sold them back to the company at a much higher price. Jin used the profit to purchase shares of Nexon Japan and sold them again for 12.6 billion won ($11 million) last year.
Jin, who was a vice ministerial-level official in the prosecution office, became the country's most senior-level incumbent prosecutor to be arrested in July. The prosecution office dismissed him in August.